core: convert (*Blockchain).JumpToState to a callback

We don't need this method to be exposed, the only its user is the
StateSync module. At the same time StateSync module manages its state by
itself which guarantees that (*Blockchain).jumpToState will be called
with proper StateSync stage.

pkg/core/blockchainer/blockchainer.go

@@ -60,7 +60,6 @@ type Blockchainer interface {
 	GetStorageItems(id int32) (map[string]state.StorageItem, error)
 	GetTestVM(t trigger.Type, tx *transaction.Transaction, b *block.Block) *vm.VM
 	GetTransaction(util.Uint256) (*transaction.Transaction, uint32, error)
-	JumpToState(module StateSync) error
 	SetOracle(service services.Oracle)
 	mempool.Feer // fee interface
 	ManagementContractHash() util.Uint160